The present invention relates to a polymer and a composition suitable for producing a cured coating resistant to environmental etch, a process for making the composition, a process for coating the substrate with the composition, and to a substrate having a coating which is resistant to environmental etching. More particularly, the present invention utilizes polymers produced from one or more sterically-hindered monomers which are capable of copolymerizing under the reaction conditions employed.
The use of addition polymers such as acrylic polymers in coatings formulations, particularly in topcoats for the automotive market, has been widespread. One of the primary requirements of such a coating for the automotive market is that it be durable. That is, the coating must resist degradation due to environmental elements which it comes into contact with, such as sunlight, gasoline, and environmental fallout such as dew, rain, or particulate matter of any kind. It has been recognized that prior art coating compositions are deficient in their ability to withstand degradation from elements which have generally and unanalytically been lumped together in the category of "environmental" causes of degradation. This sort of degradation has manifested itself in an etching or pitting of the coating's surface, and has resulted in the necessity of the automotive manufacturers to repair the coatings under warranty claims. However, in spite of the recognized deficiencies of prior art polymers and coating compositions, as well as economic penalty of such deficiencies, a long felt need for such a polymer for producing a cured topcoat resistant to environmental etch has heretofore gone unsatisfied.
The present invention provides a process of coating a substrate suitable for producing cured coatings resistant to environmental etch. In general, the coating composition comprises a sterically-hindered monomer which is ethylenically unsaturated and an ethylenically unsaturated comonomer having a functional site capable of undergoing crosslinking after the resin is formed. The amount of the sterically-hindered monomer reacted may range from about 20 to 80 weight percent, based on the total weight of the polymer. The theoretical T.sub.g (i.e., glass transition temperature) of the polymer may range from about 10.degree. C. to about 70.degree. C. This polymer may be utilized in forming a coating composition along with other reactive components.